Berlin 2005 – wissenschaftliches Programm
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MO: Molekülphysik
MO 33: Quantum Control I
MO 33.7: Vortrag
Montag, 7. März 2005, 15:45–16:00, HU 2091
Photodissociation studies of state-selected molecular ions by velocity map ion imaging — •N. Hendrik Nahler, Olivier P.J. Vieuxmaire, Alexander Webb, and Michael N.R. Ashfold — University of Bristol, School of Chemistry, Bristol BS8 1TS, UK
High resolution ion imaging methods have been used to study the photodissociation of ground state Br2+ (2Πg) and BrCl+ (2Π) cations, with spin-orbit state specificity, monitoring 79Br+ and 35Cl+ fragments as appropriate. Further studies are carried out on small polyatomic molecular ions, e.g. NH3+ and OCS+. The state-selected molecular ions are prepared by a 2+1 REMPI scheme and than dissociated by absorption of a single photon from a second tunable dye laser. Image analysis allows precise determination of the dissociation energies of ground state ions and values for the respective spin-orbit splitting constants. These experiments also provide information on the angular anisotropy of the product channels and their branching ratios.
The dissociation channels from BrCl+ show predominantly parallel character. Branching ratios into the various Br+ (3PJ) and Cl (2PJ) channels will be presented and discussed in the context of the various participating excited state potentials. Three photon excitation of BrCl resonance enhanced at the two photon energy by (2Π1/2)5sσ, v≥0 levels also generates superexcited BrCl molecules which dissociate to form Br(*) + Cl** products. The Cl** atoms are ionized by further photon absorption. The Br + Cl** products show angular distributions characterized by P2, P4, and P6 terms; this we attribute to a Σ→→Π→Π transition in BrCl.